Conventional polysilicon resistors fabricated with various types of dopants are widely use in CMOS silicon chip applications. The resistors provide known relationships between voltages applied across the resistors and currents flowing through the resistors. Doping levels established during the fabrication process vary from run to run and/or from side to side on a wafer. Therefore, unit square resistances among many polysilicon resistors vary widely, in many cases by as much as ±20 percent.
Absolute resistor values play roles in the operations of many types of circuits. Although a dependence on the absolute resistor value is eliminated in many circuit designs by using ratios of resistors, many circuit aspects rely on the absolute value of the polysilicon resistors. Conventional techniques for verification of the resistance values usually use an external precision resistor during a test phase to measure and trim the polysilicon resistors. Use of the external precision resistor increases test time.
It would be desirable to implement a method and/or apparatus for on-die verification of a resistor fabricated in a CMOS process.